Originally published on fastradius.com on March 23, 2022
Injection molding involves injecting molten plastic into carefully designed molds before cooling and ejecting the final part. It’s a highly repeatable process that enables companies to create high volumes of identical plastic parts with good tolerances at a low cost per part.
Injection molding has numerous applications in a wide variety of industries — from the automotive industry to the medical industry — but it isn’t the best choice for every project. Before you decide whether or not to injection mold your part, carefully consider the injection molding pros and cons.
Many manufacturers turn to injection molding because:
Injection molding allows for large volumes of uniform, complex parts. However, you must pay attention to vent and gate placements, weld lines, corner transitions, wall thickness, rib and boss design, and more to ease ejection and achieve precise parts.
With injection molding, you can easily achieve repeatable part tolerances of ± 0.500 mm (0.020’’). In some cases, you can even produce parts with tolerances of ± 0.125 mm (0.005’’), giving you parts that are accurate enough for most applications and comparable to 3D-printed or CNC machined parts.
Today, there are over 25,000 engineered materials that are compatible with injection molding, including thermoplastics, thermosets, resins, and silicones. With all of these options, you’ll be able to find one that offers the right balance of physical, mechanical, and chemical properties. Commonly used materials include acrylonitrile butadiene styrene (ABS), polyethylene (PE), polystyrene (PS), and polypropylene (PP). You can also use a mixture of materials to produce a part with the strength, impact resistance, or stiffness you need. For example, you might add glass fibers to your thermoplastic to create a strength-enhancing composite.
You also have a variety of options when it comes to colors. Consider using masterbatches, pre-colored resins, liquid colorants, or salt and pepper blends to achieve your desired color.
While it can take several minutes — or even hours — to 3D print or CNC machine a single part, most injection molding cycles only last 10 to 60 seconds. Even if you have a complex geometry that takes around 120 seconds to mold, you can include several smaller parts in one larger mold. This helps maximize efficiency and gets the most out of each mold, allowing you to create hundreds of identical parts an hour at a low cost.
One of the main benefits of plastic injection molding is its high repeatability. Once you’ve created your mold, you can produce thousands of parts before needing to maintain your tooling. An aluminum mold will generally last between 5,000 and 10,000 cycles, and a full-scale steel production mold can last for over 100,000 cycles. Plus, since injection molding uses the same mold for each part, you’ll have identical products.
Though injection molding generates less post-production material waste than many other manufacturing processes, it still creates excess scraps. However, you can easily regrind, melt, and reuse any sprues, runners, or other leftover plastic parts to save on material and reduce material waste.
There are plenty of advantages of plastic injection molding, but it’s not without its drawbacks. Some disadvantages include:
Since custom tooling must be created for each injection molded part, initial start-up costs are high and this isn’t economical for low-volume production runs. Tooling for a simple design and a small production run can cost between $2,000 and $5,000, but tooling for large, complex molds ready for full-scale production can cost several times that. Although you can reuse these molds again and again and save on tooling costs down the line, it’s worth considering how much molds cost upfront. An injection molding manufacturing partner can help you maximize your budget and refine your mold design so you can produce the best possible part for the best price.
A CNC machined part can be delivered within 5-10 days, and industrially 3D printed parts often have lead times of 3-5 days. However, injection molding has a longer lead time. It often takes 5-7 weeks to manufacture tooling and 2-4 weeks to produce and ship parts.
In part, this long lead time can be attributed to the complexity of the molds themselves. In addition to containing the negative of the part, these molds have complex runner and water cooling systems to facilitate material flow and faster cooling. It can take months of design and testing before the final mold is ready for production, and any design changes can further increase turnaround times.
With the help of a manufacturing partner’s expertise, you can avoid falling into common mold pitfalls that might set you back weeks and thousands of dollars. They can also help accelerate the design, testing, and production phases.
With 3D printing, you can simply upload a file and print a new part whenever you make a design change, but that’s not the case with injection molding. If you make a design change, you’ll likely need to create a new mold from scratch, which means pouring more time and money into your project.
To avoid costly design changes and ease the demolding process, avoid undercuts and sharp edges, ensure wall thicknesses are uniform, and add draft angles. If you need some guidance, an experienced manufacturing partner can offer expert design advice.
Between its efficiency and high repeatability, injection molding has plenty to offer. However, it’s all too easy to make an expensive mistake that sets production back weeks. That’s where a trusted manufacturing partner can help.
When you work with SyBridge, our team of experts can guide you through the entire production process and answer any questions you have about injection molding’s advantages and disadvantages. Ready to get started? Contact us today.
Injection moulding is one of the most commonly used methods of producing identical plastic products in high volumes. However, as with every process, it is important to understand the specific design restrictions that must be adhered to in order to facilitate the obvious benefits of successfully producing cost-effective, high-quality parts.
To help, we have very simply laid out the advantages and disadvantages to consider.
Please be aware, however, that the following guidelines apply to what we would consider to be conventional injection moulding (quantities of 100,000+) and may appear at first glance to be fairly prohibitive if you are looking to develop a product with numbers out of this norm.
The good news is Plunkett Associates have spent many years developing strategies and techniques in order to take away some of the issues identified below, particularly for parts that would traditionally be considered too difficult or unusual to mould.
In addition, we are specialists in making injection moulding far more cost effective for much lower quantities of parts than is more commonly expected. Using a hybrid of techniques, our low volume production tooling allows us to customise to client/geometry/quantities. The result is a mould tool that reflects the requirement and opens up an exciting option to produce high quality, yet low volume components.
As an ISO:9001:2015 Quality System certified supplier, we are confident we can help with your requirements, so please feel free to give us a call.
1) Fast production and highly efficient. Injection moulding can produce an incredible amount of parts per hour. Speed depends on the complexity and size of the mould, anywhere between 15-120 seconds per cycle time.
2) Low labour costs. Plastic injection moulding is an automated process whereby a majority of the process is performed by machines and robotics, which a sole operator can control and manage. Automation helps to reduce manufacturing costs, as the overheads are significantly reduced.
3) Design flexibility. The moulds themselves are subjected to extremely high pressure. As a result, the plastic within the moulds is pressed harder and allows for a large amount of detail to be imprinted onto the part and for complex or intricate shapes to be manufactured.
4) High-output production. Thousands of parts can be produced before the tooling needs to be maintained.
5) Large material choice. There is a large selection of polymer resins to choose from. Multiple plastic materials can also be used simultaneously; for example, TPE can be overmoulded onto PP parts.
6) Low scrap rates. Injection moulding produces very little post-production scrap relative to traditional manufacturing processes. Any waste plastic typically comes from the sprue and runners. Any unused or waste plastic, however, can be reground and recycled for future use.
7) Ability to include inserts. Metal or plastic inserts can be insert moulded.
8) Good colour control. Plastic parts can be manufactured in any required colours with the use of masterbatches or compounding.
9) Product consistency. Injection Moulding is a repeatable process; in other words, the second part you produce is going to be identical to the first one etc. This is a huge advantage when trying to produce high tolerances and part reliability in high volumes.
10) Reduced finishing requirements. There is often very little post-production work required as parts usually have a good finished look upon ejection.
11) Enhanced Strength. When plastic injection moulding, it is possible to use fillers in the moulding material. These fillers reduce the density of the plastic whilst it is being moulded, and can help add greater strength to the completed part.
1) High tooling costs and long set up lead times. Up-front costs are high due to the design, testing, and tooling required. There is the initial design and prototyping (probably via CNC or 3D printing), then the design of a prototype mould tool to produce replicas of the part in volume. Lastly, and only after extensive testing during both stages, you can finally injection mould a part.
2) Part design restrictions. Plastic parts must be designed with injection moulding consideration and must follow the basic rules of injection moulding, for example:
Don’t forget, because tools are typically made from steel or aluminium, it can be difficult to make design changes. If you need to add plastic to the part, you can make the tool cavity larger by cutting away steel or aluminium. But in order to take away plastic, you need to decrease the size of the tool cavity by adding aluminium or metal to it. This is extremely difficult and in many cases might mean scrapping the tool (or part of it) and starting over.
Also, the weight and size of the part will determine the tool size and necessary press size. The larger the part, the more difficult and expensive it will be.
3) Small runs of parts can be costly. Due to the complexity of tooling, and the necessity to rid the machine of all previous material before the next product can be made, the setup time can be quite lengthy. Therefore small runs of parts have traditionally always been thought of as too expensive to injection mould.
Injection moulding is a great process! The range of materials and colours is huge, and there is no “abs like’ that we get in 3D Printing, it’s the real thing. Parts are repeatable and tight tolerance. The only potential downside is the tooling, but as we said at the beginning of this article, we’ve got that covered, with options to suit most requirements.
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